23 February 2010

16 February 2010

Adding to an alreadybountiful set of crustacean conferences around the globe, the close of the year will see a conference on freshwater decapod crustaceans in Frankfurt, Germany. The organizers cite an “upsurge of interest in recent years” and that “significant numbers of species around the world are threatened with extinction” as reasons for this conference.

09 February 2010

04 February 2010

The sensory abilities of vertebrates and invertebrates are generally more similar than they are different: both groups can detect light, sound, pressure, and so on. One of the few cases of a sensory ability that seemed to be the domain of vertebrates alone was the ability to detect electrical signals: electroreception. Several fish have it, and use electrical signals to communicate. Platypus have it. Electric signaling in fish is a classic examples of behaviour understood at the neural level.

For a long time, people argued that invertebrates don’t have electroreception, for reasons that were perhaps a bit idiosyncratic. One explanation I heard given was that something like a crayfish was too small.

A few years ago, a couple of papers came out that started to pick apart that idea, and showed that crayfish could respond to electrical signals. This new paper by Patullo and Macmillan* pushes the state of the art forward in a couple of ways.

First, it expands the number of species. The authors used Cherax destructor, which they’d used in a previous study, and also tested Cherax quadricarinatus (pictured). Both species decreased their activity in the presence of electric fields, at about the same intensity levels.

The intensity levels were the second way this paper pushed things forward: it showed that crayfish were responding to much lower levels of electricity than previous studies – about ten times lower. Because neurons run on electricity, if you give an intense enough signal, animals will respond, even if they have no specialized sensory apparatus for detecting electical fields. This paper goes further towards suggesting that crayfish can respond to a biologically relevant electrical signal. And, indeed, one of the key features is that the electrical signal played to the crayfish was derived from a swimming tadpole, which crayfish will prey upon.

These experiments seem rather tricky to pull off and calibrate. Behavioural analysis is complicated by there not be any particular behaviour identified (yet!) that is reliably and consistently evoked by an electrical signal. This is going to make the next stage of this research, locating the neurons responsible for crayfish electroreception, a challenge.

*Full disclosure: I have worked with both authors on this paper, so I think of them as Blair and David.

02 February 2010

Ireland is worried about its crayfish, according to this nice pamphlet. And with good reason. It's the only place in Europe that doesn’t have any known populations of non-native crayfish species.

Yet.

The brochure is mainly about crayfish plague, which has hit the native Irish crayfish populations occasionally. (The Irish, after all, have some experience with fungal pathogens.) It says this of Marmorkrebs:

Perhaps the most dangerous is the ‘Marmokrebs’ or Marbled Crayfish, an Orconectes clone which is parthenogenetic, i.e. it can reproduce without mating, and produces large numbers of offspring. These have already been dumped into the wild in two European countries, and a bucket of them was recently intercepted in UK.

I have no idea where the idea that Marmorkrebs are related to Orconectes came from. Absolutely every scientific paper has placed them in the genus Procambarus. (I emailed them about it, so they know for the brochure reprint, though. Please don’t hassle them any more.)

Marmorkrebs are parthenogenetic marbled crayfish whose origins are unknown. They have potential to be a model organism for biological research because they are genetically uniform, and to be an invasive pest species. Maintaining self-sustaining breeding colonies is a key element of most successful model organisms. We tried to find the best conditions for establishing and maintaining a Marmorkrebs breeding colony for research. Marmorkrebs can be bred in a compact tank system originally designed for zebrafish. Occasional use of live food (Artemia nauplii) did not significantly enhance growth of Marmorkrebs compared to an Artemia replacement. The presence of shelters did not affect growth of Marmorkrebs. High juvenile mortality poses the most significant obstacle to establishing a self-sustaining research colony of Marmorkrebs, although relatively few adults would be needed to supply many viable embryos for developmental research.